Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$112.35	6.591%	$119.755	$119.76	$119.75	$119.80
Purchase #2	$62.36	11.568%	$69.5738	$69.57	$69.55	$69.60
Purchase #3	$249.38	11.492%	$278.0387	$278.04	$278.05	$278.00
Purchase #4	$205.50	9.806%	$225.6513	$225.65	$225.65	$225.70
Purchase #5	$100.61	10.590%	$111.2646	$111.26	$111.25	$111.30
Purchase #6	$89.50	11.391%	$99.6949	$99.69	$99.70	$99.70
Purchase #7	$62.75	10.644%	$69.4291	$69.43	$69.45	$69.40
7 purchase totals =	$882.45		$973.4074	$973.40	$973.40	$973.50